WARNING: This document has been retracted by the author(s). Implementation of the protocol described herein is not recommended. Developers desiring similar functionality are advised to implement the protocol that supersedes this one
(if any).

Actuators are devices in sensor networks that can be controlled through the network and act with the outside world. In sensor networks and Internet of Things applications,
actuators make it possible to automate real-world processes. This document defines a mechanism whereby actuators can be controlled in XMPP-based sensor networks, making it
possible to integrate sensors and actuators of different brands, makes and models into larger Internet of Things applications.

Note has to be taken, that these XEP's are designed for implementation in sensors, many of which have very limited amount of memory (both RAM and ROM) or resources (processing power).
Therefore, simplicity is of utmost importance. Furthermore, sensor networks can become huge, easily with millions of devices in peer-to-peer networks.

Sensor networks contains many different architectures and use cases. For this reason, the sensor network standards have been divided into multiple XEPs according to the following table:

Table 1: Sensor Network XEPs

XEP

Description

xep-0000-IoT-BatteryPoweredSensors

Defines how to handle the peculiars related to battery powered devices, and other devices intermittently available on the network.

xep-0000-IoT-Discovery

Defines the peculiars of sensor discovery in sensor networks. Apart from discovering sensors by JID, it also defines how to discover sensors based on location, etc.

Defines guidelines for how to achieve interoperability in sensor networks, publishing interoperability interfaces for different types of devices.

xep-0000-IoT-Multicast

Defines how sensor data can be multicast in efficient ways.

xep-0000-IoT-PubSub

Defines how efficient publication of sensor data can be made in sensor networks.

xep-0000-IoT-Chat

Defines how human-to-machine interfaces should be constructed using chat messages to be user friendly, automatable and consistent with other IoT extensions and possible underlying architecture.

XEP-0322

Defines how to EXI can be used in XMPP to achieve efficient compression of data. Albeit not a sensor network specific XEP, this XEP should be considered
in all sensor network implementations where memory and packet size is an issue.

XEP-0323

Provides the underlying architecture, basic operations and data structures for sensor data communication over XMPP networks.
It includes a hardware abstraction model, removing any technical detail implemented in underlying technologies. This XEP is used by all other sensor network XEPs.

XEP-0324

Defines how provisioning, the management of access privileges, etc., can be efficiently and easily implemented.

XEP-0325

This specification. Defines how to control actuators and other devices in Internet of Things.

A momentary value represents a value measured at the time of the read-out.

Node

Graphs contain nodes and edges between nodes. In Internet of Things, sensors, actuators, meters, devices, gatewats, etc., are often depicted as nodes whereas links between sensors (friendships)
are depicted as edges. In abstract terms, it's easier to talk about a Node, rather than list different possible node types (sensors, actuators, meters, devices, gateways, etc.).
Each Node has a Node ID.

Node ID

An ID uniquely identifying a node within its corresponding context. If a globally unique ID is desired, an architecture should be used using a universally accepted
ID scheme.

Parameter

Readable and/or writable property on a node/device. The XEP-0326 Internet of Things - Concentrators (XEP-0326) [5] deals with reading and writing parameters
on nodes/devices. Fields are not parameters, and parameters are not fields.

Peak Value

A maximum or minimum value during a given period.

Precision

In physics, precision determines the number of digits of precision. In sensor networks however, this definition is not easily applicable. Instead, precision
determines, for example, the number of decimals of precision, or power of precision. Example: 123.200 MWh contains 3 decimals of precision. All entities parsing and
delivering field information in sensor networks should always retain the number of decimals in a message.

Sensor

Device measuring at least one digital value (0 or 1) or analog value (value with precision and physical unit). Examples: Temperature sensor, pressure sensor, etc.
Sensor values are reported as fields during read-out. Each sensor has a unique Node ID.

SN

Sensor Network. A network consisting, but not limited to sensors, where transport and use of sensor data is of primary concern. A sensor network may contain actuators, network applications, monitors, services, etc.

Status Value

A value displaying status information about something.

Timestamp

Timestamp of value, when the value was sampled or recorded.

Token

A client, device or user can get a token from a provisioning server. These tokens can be included in requests to other entities in the network, so these entities can validate
access rights with the provisioning server.

Unit

Physical unit of value. Example: MWh, l/s, etc.

Value

A field value.

Value Status

Status of field value. Contains important status information for Quality of Service purposes. Examples: Ok, Error, Warning, Time Shifted, Missing, Signed, etc.

Value Type

Can be numeric, string, boolean, Date & Time, Time Span or Enumeration.

WSN

Wireless Sensor Network, a sensor network including wireless devices.

XMPP Client

Application connected to an XMPP network, having a JID. Note that sensors, as well as applications requesting sensor data can be XMPP clients.

Control in sensor networks is about setting output values. To make the implementation simple, it is assumed that control of a device can be made using a single message.
If only a simple set operation is requested, a <message> stanza can be sent. If an acknowledgement (ACK) of the operation (or Not-acknowledgement NACK) of the operation
is desired, an <iq> stanza can be used instead.

To set control parameters in a device, the set command is sent to the device. The set command allows for two different ways of setting control parameters:

Using strongly typed parameters. This way performs best in EXI compression and automation.

Using a weakly typed data form. This might be better for manually setting control parameters, since it allows the device to give the user a better user interface explaining
available control parameters.

What type of control parameters there are available in different types of devices is described in
[6].

If the device is a concentrator, as defined in Internet of Things - Concentrators,
an handles multiple nodes behind it, which node(s) to control is defined using node elements. If not a concentrator,
the use of node elements is not necessary, and control commands are sent directly to the device itself.

Note that any response is supressed when sending a message stanza, regardless if the desired control command could be executed or not. The following example shows how the same
control command could be issued using an IQ stanza instead:

Note: An empty setResponse element means that the control command was executed as provided in the request. Sometimes, the device
can restrict the command to a subset of nodes and/or parameters. In such cases, the setResponse element will contain what nodes and/or parameters
were finally used to perform the command. For examples of this, see Internet of Things - Provisioning (XEP-0324) [7].

In the following use cases, often a message stanza will be used to illustrate the point. However, the same operation could equally well be used using an iq stanza instead.

By using an IQ stanza, the caller can receive an acknowledgement of the reception of the command, or error information if the command could not be processed.
Following is an example of a control command sent using an iq stanza, where the receiver reports an error back to the caller:

Setting single integer-valued control parameters is a common use case, for instance when controlling analog outputs. Even though 32-bit integers may cover most control needs,
it might in some cases be limiting. Therefore, a 64-bit control parameters can be created. The following example shows how a 64-bit integer value
can be set in a device.

Setting date & time-valued control parameters might be necessary when timing is an issue. Often it forms part of a larger context.
The following example shows how a date & time value can be set in a device.

Setting single color values in a device can occur in instances where color or lighting is important. Sometimes color is set using enumerations (string-valued
or integer-valued parameters), and sometimes as a color property. The following example shows how a color value can be set in a device.

Often, setting a single control parameter is not sufficient for a control action. In these cases, setting multiple control parameters at once is necessary.
The set command makes this easy however, since it allows for any number of control parameters to be set at once, as the following example shows:

Sometimes the order of control parameters are important in the device, and sometimes the parameters form part of a whole. It depends on the context of the device.
In the above example, the order is important. When the OutputPercent control parameter is set, it will start to fade in or out to the desired setting (10%), using the
fade time set previously. If the FadeTimeMilliseconds control parameter would have been set after the OutputPercent parameter, the fading would have been started using
the previous setting, which might be unknown.

The order of control parameters to use depends on the device. The Control Form lists available control parameters of the device in the
order they are expected to be sent to the device. The XEP xep-0000-IoT-Interoperability details what control parameters
must be available for different interfaces, and if the order of control parameters is important.

IMPORTANT: The device MUST mark all control parameters in the form as notSame, as defined in
[8]. If an end user would open the control form and press OK (submitting the form) without having entered a value, no value
would be written, and no action taken. If only a few parameter would be edited, only those parameters would be sent to the device
and only the corresponding actions taken.

All parameters in the form MUST also have validation rules defined according to XEP-0122,
specifically validation data types and ranges where appropriate. This to give type information to the client, which the client later can use to send
typed control commands directly, without the need to get and send data forms to the device to control it.

Also, the device SHOULD group control parameters that should be written together using pages and sections, as described in
XEP-0141. Parameters
MUST also be ordered in a way so that when set in that order using the typed commands, the corresponding control actions can be successfully executed.

Control actions can be requested by submitting a full or partial control form back to the device. Control parameters not edited MUST not be included
in the form, and the device in turn MUST ONLY invoke control actions corresponding to the parameters returned in the form.

The following example shows how control actions can be requested submitting a control parameters form to the device:

In this example, the FadeTimeMilliseconds and OutputPercent control parameters are sent, while the MainSwitch control parameter is left as is. Fading is therefore
parformed only if the dimmer is switched on.

A device can reject a control form submission. It does this returning an error iq stanza. If there are errors in the form, details are listed
using paramError elements in the response, as is shown in the following example:

Controlling devices behind a concentrator can be done by specifying what device(s) to control using node elements within the
command elements sent to the concentrator. The following sub-sections show examples of how this is done.

By using an IQ stanza, the caller can receive an acknowledgement of the reception of the command, or error information if the command could not be processed.
When sending a control command to multiple nodes at a time the device must validate all parameters against all nodes before taking any control action. If
validation fails, an error message is returned and no control action is taken. The following example shows an example of an erroneous control message made to
multiple nodes on a device:

A client can get a control form containing available control parameters common between a set of nodes controlled by the concentrator. This is done
adding a sequence of node elements to a getForm command sent to the concentrator, as is shown in the following example:

A device can reject a control form request. It does this returning an error iq stanza. The following example shows the device rejecting
a control form request, because it does not support the handling of common parameters between multiple nodes:

A device can reject a control form submission. It does this returning an error iq stanza. The following example shows the device rejecting a
control form submission because one of the control parameters, even though it exists on all nodes, is not of the same type on all nodes.

In order for an application to determine whether an entity supports this protocol, where possible it SHOULD use the dynamic, presence-based profile of service discovery defined
in Entity Capabilities (XEP-0115) [10]. However, if an application has not received entity capabilities information from an entity, it SHOULD use explicit service discovery instead.

Depending on the reason for rejecting a control request, different XMPP errors can be returned, according to the description in the following table. The table also
lists recommended error type for each error. Error stanzas may also include paramError child elements to provide additional textual error information that
corresponds to a particular control parameter provided in the request. Any custom error message not related to control parameters is returned in a text
element.

Table 2: XMPP Errors when rejecting a readout request

Error Type

Error Element

Namespace

Description

cancel

forbidden

urn:ietf:params:xml:ns:xmpp-stanzas

If the caller lacks privileges to perform the action.

cancel

item-not-found

urn:ietf:params:xml:ns:xmpp-stanzas

If an item, parameter or data source could not be found.

modify

bad-request

urn:ietf:params:xml:ns:xmpp-stanzas

If the request was malformed. Examples can include trying to set a parameter to a value outside the allowed range.

cancel

feature-not-implemented

urn:ietf:params:xml:ns:xmpp-stanzas

If an action has not been implemented in the device.

wait

conflict

urn:ietf:params:xml:ns:xmpp-stanzas

If an item was locked by another user or process and could not be accessed. The operation can be retried at a later point in time.

The simplest way to read the current control states of a device, is to request the control form of the device. The control form should contain the current
values for all avilable control parameters. However, since current states might not be available at the time of the request, the states might be delivered
asynchronously, using messages defined in Data Forms - Dynamic Forms (XEP-0336) [11].

Using this method has the advantage that a small actuator device does not need to implement other XEPs to support readout of current control states. If the device
contains all current states readily accessible, there's no need of asynchronous updates making readout simple and straightforward.

A second option is to use Internet of Things - Sensor Data (XEP-0323) [12] to deliver current control states. Since this XEP contains mechanisms allowing for asynchronous readout of control parameter
states. This makes readout of such parameters simpler. However, there's a need to map values between the two XEPs.

If a client wants to know the current status of control parameters using this method, it performs a readout of Momentary and Status values
from the device, and from the returned set of values take the current control parameter value according to the following rules, ordered by priority:

If there's a field marked as momentary value, with an unlocalized field name equal to the unlocalized control parameter name and having a compatible
field value type (see table below) and a status field without the missing flag set, the value of the field should be considered the current value of
the control parameter.

If there's a field marked as status value, with an unlocalized field name equal to the unlocalized control parameter name and having a compatible
field value type (see table below) and a status field without the missing flag set, the value of the field should be considered the current value of
the control parameter.

To simplify mapping, a writable attribute can be used to inform the client if a field name corresponds to a control parameter or not. If the
attribute is available, it tells the client if it corresponds to a control parameter or not. If not available, no such deduction can be made.

Even though getting the the control form could provide the client with a quicker and easier way of retrieving control parameter values, the form is not
guaranteed to contain correct current values, as described above.

The following table shows how corresponding field values should be converted to the corresponding control parameter value based on field type (x-axis) and
control parameter type (y-axis). An empty cell means conversion has no meaning and types are not compatible.

Table 3: Conversion of Field Value to Control Parameter Value based on types

325 \ 323

boolean

date

dateTime

duration

enum

int

long

numeric

string

time

boolean

x

!=0

!=0

!=0

color

RRGGBB or RRGGBBAA

date

x

Date part

(1)

dateTime

x

x

(2)

double

Z2

x

x

x

(3)

duration

x

(4)

x

int

Z2

Ordinal

x

Thunk

Thunk

(5)

long

Z2

Ordinal

x

x

Thunk

(5)

string

xs:boolean

xs:date

xs:dateTime

xs:duration

x

xs:int

xs:long

(6)

x

xs:time

time

Time part

(7)

(8)

x

The following table lists notes with details on how to do conversion, if in doubt.

Table 4: Conversion rules

Note

Description

(1)

The client should try to convert the string to a date value, first according to the format specified by the XML data type xs:date, and if not possible
by RFC 822.

(2)

The client should try to convert the string to a date & time value, first according to the format specified by the XML data type xs:dateTime, and if not possible
by RFC 822.

(3)

The client should try to convert the string to a double-precision floating-point value, first according to the format specified by the XML data type xs:double,
and if not possible using system-local string to floating-point conversion using local decimal and throusand separator settings.

(4)

The client should try to convert the string to a duration value, first according to the format specified by the XML data type xs:duration,
and if not possible using the XML data type xs:time.

(5)

The client should try to convert the string to an integer value according to the corresponding XML data type formats xs:int and xs:long.

(6)

The numeric field value consists of three parts: Numeric value, number of decimals and optional unit. If no unit is provided, only the numeric value should
be converted to a string (compatible with the XML data type xs:double), using exactly the number of decimals provided in the field. If a unit is provided
(non-empty string) it must not be appended to the value, if the value is to be used for control output. For presentation purposes however, a space could be
appended to the number and the unit appended after the space.

(7)

A duration field value contains a xs:duration value. The xs:duration has a larger domain than xs:time, and contains all xs:time values, but xs:time does
not contain all possible xs:duration values. So, conversion of an xs:duration value to an xs:time value should be performed only if a duration lies
between 00:00:00 and 23:59:59.

(8)

The client should try to convert the string to a time value according to the format specified by the XML data type xs:time.

x

Use the canonical conversion method.

Z2

true = 1, false = 0.

!=0

Nonzero = true, Zero = false.

RRGGBB

A string of six hexadecimal characters, the first two the red component of the color, the next two the green component and the last two the blue component.

RRGGBBAA

A string of eight hexadecimal characters, the first two the red component of the color, the next two the green component, the following two the blue component and the last two the alpha channel.

Date part

Only the date part of the xs:dateTime value should be used.

Time part

Only the time part of the xs:dateTime value should be used.

Ordinal

Each enumeration value may in the implementation correspond to an ordinal number.

Thunk

The value is thunked down to lower precision in the canonical way.

xs:boolean

Conversion to a string should follow the rules specified for the XML datatype xs:boolean.

xs:dateTime

Conversion to a string should follow the rules specified for the XML datatype xs:dateTime.

xs:duration

Conversion to a string should follow the rules specified for the XML datatype xs:duration.

When representing control parameters as momentary field values, it is important to note the similarities and differences between XEP-0323 (Sensor Data) and XEP-0325 (this document):

The enum field value data type is not available in XEP-0325 (this document). Instead enumeration valued parameters are represented as string control
parameters, while the control form explicitly lists available options for the parameter. Options are not available in XEP-0323, since it would not be practical to list all options
every time the corresponding parameter was read out. Instead, the enum element contains a data type attribute, that can be used to identify the type of the enumeration.

The numeric field value data type is not available in XEP-0325 (this document). The reason is that a controller is not assumed to understand unit conversion. Any
floating-point valued control parameters are represented by double control parameters, which lack a unit attribute. They are assumed to have the same unit as
the corresponding numeric field value. On the other hand, floating point valued control parameters without units, are reported using the numeric
field element, but leaving the unit blank.

Control pameters of type color have no corresponding field value data type. The color value must be represented in another way, and is implementation specific.
Possibilities include representing the color as a string, using a specific pattern (for instance RRGGBBAA), or report it using multiple fields, one for each component for instance.

The boolean, date, dateTime, duration, int, long, string
and time field value data types correspond to control parameters having the same types and same element names.

A node defined in a concentrator, as defined by Internet of Things - Concentrators, supporting control has
two sets of parameters that are different: First a set of node parameters and then a set of control parameters.

Node parameters are defined by the node type in the concentrator, as described in Internet of Things - Concentrators,
and they are typically used by the concentrator to define the node and how to communicate or interact with the underlying device. The important part here is to know
that the node parameters are maintained by the concentrator, not the underlying device.

Control parameters however, are parameters that reside on the underlying device. When set, they change the actual state or behaviour of the underlying device.
The connection to the device however, controlled by the concentrator, remains unchanged by such a control parameter update.

Many control actions available in a device can be controlled using only one control parameter. If a device only publishes such control parameters, the order
of control parameters is not that important.

However, there are many control actions that require the client to set multiple control parameters at the same time, for the device to have a complete understanding
what the client wants to do.

XEP-0141 defines a way to group parameters in a data form by including the concept of pages and sections.
Even though these pages and sections are used for layout purposes, it should be used by devices to mark parameters that should be used together to perform control actions.

The following set of rules should be adhered to, by devices as well as clients, to minimize confusion and resulting errors:

Control parameters should be listed in control forms in the order the device expects the client to write them back.

Clients should set control parameters in the order they are listed in the corresponding control forms.

Control actions that require multiple control parameters should report these together, grouped by pages or sections within pages,
to make clear that the parameters belong together.

For control actions requiring multiple control parameters, devices should strive to publish default values for all parameters involved.
These default values should then be used by the device if a client happens to write only a subset of the control parameters required for
a control action. The default value could be the current state of the parameter.

Note however, that one cannot always make the assumption that parameters on the same page or same section in a control form belong to the same control action.
For instance, a PLC with 16 digital outputs might publish a control form containing a single page with 16 check boxes on (boolean parameters), that can be
controlled individually.

To solve the problem of grouping parameters together, so a client can know which parameters belong together, a new element is defined that can be used in
data forms: parameterGroup. It is optional, but can be added to control parameters in forms, as a way to tell the client that parameters
having the same parameterGroup belong together and should be written together.

Note: If used, the server must not include a parameter in more than one parameter group at a time. The form may contain multiple group, but each
parameter must only have at most one parameterGroup element.

The following example illustrates the use of the parameterGroup element to group parameters together.

However, there are many differences between Node Commands and Control Parameters, as shown in the following list:

Node Commands are defined by the node type in the concentrator, and not by the device itself.

Node Commands may do many different things, not only performing control actions.

Parametrized Node Commands require the client to always get a parameter data form, and write back values. There's no way to send simple
control messages using Node Commands.

Node Commands can be partitioned, grouped and sorted separately.

Each Parametrized Node Command has a separate parameter form, which makes grouping of parameters normal.

Node Commands are only available for nodes controlled by a concentrator.

If implementing a device with many complex control actions (like an advanced PLC), consideration should be made to divide the device into logical groups and
implement the concentrators interface as well. Then the more complex control actions could be implemented as Node Commands instead of control actions
as defined in this document, and implementing the simpler more intuitive control actions as described in this document.

If control interaction is performed in a context of delegated trust, as defined in the Sensor Network Provisioning XEP-0324 Internet of Things - Provisioning (XEP-0324) [7],
tokens should always be included in all calls. This to allow devices to check privileges with provisioning servers.

Most examples in this document have been simplified examples where a few devices containing a few control parameters have been used. However, in many cases large subsystems with
very many actuators containing many different control actions have to be controlled, as is documented in
Internet of Things - Concentrators.
In such cases, a node may have to be specified using two or perhaps even three ID's: a sourceId identifying the data source controlling the device, a possible
cacheType narrowing down the search to a specific kind of node, and the common nodeId. For more information about this, see
Internet of Things - Concentrators.

Note: For cases where the nodeId is sufficient to uniquely identify the node, it is sufficient to provide this attribute in the request.
If there is ambiguity in the request, the receptor must treat the request as a request with a set of nodes, all with the corresponding nodeId as requested.

All timestamps and dateTime values use the XML data type xs:dateTime to specify values. These values include a date, an optional time and an optional time zone.

Note: If time zone is not available, it is supposed to be undefined. The client reading the sensor that reports fields without time zone information
should assume the sensor has the same time zone as the client, if not explicitly configured otherwise on the client side.

If devices report time zone, this information should be propagated throughout the system. Otherwise, comparing timestamps from different time zones will be impossible.

Control commands sent using IQ stanzas instead of messages, should consider using the xml:lang attribute to specify the desired language
used (if possible) when returning information back to the caller, like error messages, localized control forms, etc.

Controlling devices in a large sensor network is a hackers wet dream. Therefore, consideration of how network security is implemented should not be underestimated.
The following sections provide some general items that should be considered.

Consider using provisioning servers to allow for detailed control of who can do what in a sensor network. Implementing proper provisioning support decreases
the risk for adverse effects, not only from intentional hacking, but also from unintentional errors.

If using delegated trust, make sure the provisioning servers are properly authenticated and validated before trusting them.

Appendix C: Legal Notices

Copyright

Permissions

Permission is hereby granted, free of charge, to any person obtaining a copy of this specification (the "Specification"), to make use of the Specification without restriction, including without limitation the rights to implement the Specification in a software program, deploy the Specification in a network service, and copy, modify, merge, publish, translate, distribute, sublicense, or sell copies of the Specification, and to permit persons to whom the Specification is furnished to do so, subject to the condition that the foregoing copyright notice and this permission notice shall be included in all copies or substantial portions of the Specification. Unless separate permission is granted, modified works that are redistributed shall not contain misleading information regarding the authors, title, number, or publisher of the Specification, and shall not claim endorsement of the modified works by the authors, any organization or project to which the authors belong, or the XMPP Standards Foundation.

Disclaimer of Warranty

## NOTE WELL: This Specification is provided on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE. ##

Limitation of Liability

In no event and under no legal theory, whether in tort (including negligence), contract, or otherwise, unless required by applicable law (such as deliberate and grossly negligent acts) or agreed to in writing, shall the XMPP Standards Foundation or any author of this Specification be liable for damages, including any direct, indirect, special, incidental, or consequential damages of any character arising from, out of, or in connection with the Specification or the implementation, deployment, or other use of the Specification (including but not limited to damages for loss of goodwill, work stoppage, computer failure or malfunction, or any and all other commercial damages or losses), even if the XMPP Standards Foundation or such author has been advised of the possibility of such damages.

IPR Conformance

This XMPP Extension Protocol has been contributed in full conformance with the XSF's Intellectual Property Rights Policy (a copy of which can be found at <https://xmpp.org/about/xsf/ipr-policy> or obtained by writing to XMPP Standards Foundation, P.O. Box 787, Parker, CO 80134 USA).

Appendix D: Relation to XMPP

The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 6120) and XMPP IM (RFC 6121) specifications contributed by the XMPP Standards Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this document has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.

Appendix E: Discussion Venue

The primary venue for discussion of XMPP Extension Protocols is the <standards@xmpp.org> discussion list.

Appendix F: Requirements Conformance

The following requirements keywords as used in this document are to be interpreted as described in RFC 2119: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".

13. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.